The Constitution is not an instrument for the government to restrain the people, it is an instrument for the people to restrain the government - lest it come to dominate our lives and interests”.- Patrick Henry

I've been curious about transformer covers for some time. In the M-500 days, the field coils had covers which were dispensed with on the M-500ts (except for some very early ones, one which I worked on).

Are the covers just decorative or do they shield EMI? In other words, is the composition of the cover important to the functioning of the amplifier?